TMK 700 multimeter

[ppppenguin]

Was clearing out a cupboard and found my old TMK 700 multimeter. It was in its original box, complete with user instructions and invoice. I bought it from Henry's Radio for £18 in 1973. A lot of money for a schoolboy in those days. It was my 2nd multimeter. The first was a smaller Japanese one that suffered badly from my inexperience. The TMK was a very useful meter. Up to 5000V AC/DC and AC current ranges. A sort of poor man's Avo.

All in excellent condition apart from 2 of the rubber feet missing. Was glad to find the batteries were absent, rather than a nasty pile of corrosion.

I used it for quite a few years until I got a secondhand Fluke 8020. Probably around 1981. Dim memory says it cost me £50. I can't remember the name of the place near Kings Cross that used to hold regular sales of secondhand testgear, some at bargain prices. I still have the 8020 and use it occasionally.

Since I haven't used the TMK700 in well over 20 years I'm thinking about flogging it on the B&B next Harpenden.

[Mike Watterson]

The 5KV range is handy for folks with valve transmitters & valve power amps. Most cheap DMMs die in a blue flash even on 750V range with 450V DC. The only thing I use an AVO for is voltages more than 350V.
Mind, that's about twice in the last 15 years!

[ppppenguin]

Not sure I'd entirely trust the 5kV range on anything with real power behind it. Some Avos had a 3kV range. I still use an EHT probe I built in 1975 when I first played with colour TV. It's 500M made from 15x 33M Mullard (as they then were) VR37 resistors "borrowed" from the stores at BBC Kingswood Warren. Plus a nominal 5M to make up the total. All enclosed in a plastic tube inside a tufnol tube. I used it with the TMK700 on 50uA. ISTR calibrating it at the BBC using a DMM that could read 1kV, a variable EHT supply and the same DMM that could read down to some small fraction of a uA.

[Mike Watterson]

I bought a bunch of 33M high voltage resistors to make a probe. I've nothing I intend measuring above about 600V. I've never measured CRT EHT, though I did work in a lab for a while testing ceramic capacitors at 50KV to 100KV intended for a Harrier headup display.

[Terry]

I had a not dissimilar looking TMK that I bought about 10 years earlier.

No 5kV range but it was 30,000Ω/Ω rather than the usual 20,000Ω/V. It should still be around somewhere.